Radiofrequency (RF) and cryogenic ablation procedures are well recognized treatments for vascular and cardiac diseases such as atrial fibrillation. The application of either RF or cryogenic treatment is usually based on the preference of the surgeon or the specific tissue to be treated. In either RF or cryogenic ablation, however, the location and quality of the lesion produced is a primary concern.
Current methods to identify a lesion's location and assess its quality include coupling a plurality of electrodes to the distal end of a medical device proximate a tissue to be treated, applying a voltage, and measuring impedance across the electrodes with the tissue to be treated completing the circuit. Electrical impedance is defined as the total opposition to alternating current by an electric circuit, equal to the square root of the sum of the squares of the resistance and reactance of the circuit and usually expressed in ohms. In general, the impedance decreases as the treated tissue becomes necrotic. As such, impedance may be used to identify particular areas which have been treated and those that have not.
One drawback to impedance tomography is its lack of direct feedback to evaluate whether a lesion was successfully created to the desired transmurality, quality, or continuity. In particular, impedance measurements provide binary data regarding a particular lesion; either the tissue is viable or necrotic. Impedance measurements alone, however, do not provide real-time assessment of whether a cryogenic or RF lesion was successfully created to a desired lesion depth, in part, because different tissue levels have different impedances.
As such, it would be desirable to provide improved methods of assessing lesion quality and depth of cryogenically and/or RF treated tissue to determine the efficacy and resulting characteristics of the treatment.